A breathing circuit delivers medical gas to a patient under pressure in a prescribed volume and breathing rate. The medical gas is often humidified by a humidifier located at or near the ventilator or respirator. The optimum respiratory circuit delivers 100% RH medical gases to the patient while reducing the amount of humidity and subsequent condensate delivered back to the ventilator through the expiratory limb. Therefore, the humidified gas has to travel through all or most of the tubing and has time to cool. Cooling of the gas leads to rainout or condensation in the breathing tube and collection of water within the breathing circuit.
Several possible solutions to the problem of rainout have been developed. One such proposed solution is a heating wire provided along the length of the tube. The wire may be provided within the interior of the tubing or alternatively may be embedded along the interior of the tubing. The wire heats the humidified gas traveling through the tubing to prevent the gas from cooling, thus preventing the problem of water condensing out of the gas traveling through the breathing circuit. However, the manufacture of such heated wire respiratory circuits can be time consuming and costly.
Another possible solution, which eliminates the heated wire, is to provide a water collection device somewhere within the breathing circuit. A water collection apparatus is typically placed in the expiratory limb of the respiratory circuit to collect and allow for manual removal of excessive condensation prior to the gases entering the ventilator or respirator. It is known that excessive condensate entering a ventilator or respirator from the expiratory limb of a respiratory circuit can harm the device.
Most frequently, the water collection device is designed to trap the condensed water vapor in a removable container. When the container is removed, a valve can be actuated to create a gas tight seal for the breathing circuit. However, this type of water collection device has to be monitored and manually emptied, causing risk of patient or caregiver infection. The removal of moisture and condensation management is not automatic. Furthermore, the removable container is often only at one discrete point along the breathing circuit, and may need to be lowered to gravitationally collect liquid, which may be impractical.
Another possible solution is to provide a permeable membrane in the breathing circuit tubing which is permeable to water vapor but impermeable to liquid water, such that moisture inside the breathing gas flow inside such tubing dissipates to outside the tubing via such a membrane, and out to the ambient air surrounding the tubing. The problem with this solution is at least two-fold: first, such a thin walled membrane which is exposed to the surroundings can be easily punctured or damaged; and second, due to a relatively high humidity in the ambient conditions, there can be a limited humidity differential between the breathing gas flow and the ambient surroundings, so that the capacity for moisture to dissipate passively through the permeable membrane to ambient surroundings can also be limited.
Accordingly, it is desirable to provide an improved apparatus for removing or decreasing water vapor, moisture, and/or condensate in a breathing circuit. It is further desirable that the improved apparatus for removing water vapor, moisture or condensate from the breathing tube, eliminates the need to monitor the device or to heat the exhalation limb of the breathing tube, and is not dependent on the positioning of the device, protects the device and its moisture and humidity transmission mechanism from damage, and increases its capacity for moisture removal and condensation management in a breathing circuit.